Nitrosoureas including BCNU, CCNU, methyl-CCNU and streptozotocin are of clinical value in the treatment of a broad spectrum of neoplasms, including CNS disease, leukemia, Hodgkin's disease and others. They have the distinct advantage of penetration of the blood-brain barrier. Present evidence favors the nucleic acids as one of the principal target sites. While much empirical structure-antileukemic activity data exists, the mode of action is not understood which is preventing rational structure modification to enhance antitumor properties. The first objective is to synthesize several suggested plausible breakdown products of the nitrosoureas and examine their properties. Secondly the chemical interaction of these compounds together with those of the parent nitrosoureas with nucleic acids will be examined. The study will employ sensitive and versatile ethidium fluorescence assays which have proven utility in the study of the modes of action of several antitumor agents. The assays permit the direct detection and quantitation of alkylation of DNA by nitrosoureas and their metabolites as well as the base specificity. Thirdly an examination will be made of the mechanism of the reported single strand scission of DNA by nitroso compounds and its bearing on carcinogenesis, mutagenesis and antitumor action. Attempts will be made to correlate extent, type and rate of chemical modifications of DNA with the antitumor properties of nitrosoureas as has been done successfully for other agents. An understanding of the chemical basis of the mode of action will be invaluable in providing the data for rational structural design to optimize antileukemic properties. The project is estimated to take 3 years for completion.